As one of the methods for measuring a three-dimensional shape, such as an the surface shape of an object, there is a method in which the surface shape of an object is measured by acquiring information on the height of each point on the surface of the object by using a confocal optical system. In the measurement using a confocal optical system, the measurement is performed, in principle, for each point, and hence a special contrivance is necessary to measure a surface area.
As this type of technique for measuring a surface area, such as the surface of an object, by using a confocal optical system, a technique is disclosed in JP-A 9-329748.
JP-A 9-329748 discloses a confocal microscope provided with a light source and a Nipkow disk in which a plurality of apertures are formed. Each of the apertures functions as a point light source and a detector. A plurality of light beams respectively having passed through the plurality of apertures are converged by an objective lens to respectively corresponding converging positions on the side of a measurement object. Therefore, when the Nipkow disk is rotated, each of the light beams (hereinafter referred to as spots) having passed through the plurality of apertures and converged at the plurality of converging positions on the side of the measurement object can be easily scanned at high speed on the surface of the measurement object.
However, it is difficult to prevent adverse effects resulting from the rotation of the Nipkow disk in the method in which the spots are scanned on the surface of the measurement object by using the Nipkow disk. Examples of the adverse effects resulting from the rotation of the Nipkow disk include the fact that the curvature of the curve of the trajectory drawn by the aperture according to the rotation of the Nipkow disk is different according to the distance from the center of the disk. The curvature of the trajectory is different for each of the apertures, and thereby a variation occurs such that the scanning speed is different for each of the apertures. Further, it is not possible to avoid rotational deflection due to the eccentricity of the disk, and to avoid vibration generated by the continuous rotation of the disk.